1. Field of the Invention
The present invention relates to a spectrum analyzer, particular an indicator mounted on a sound reproducing apparatus or the like.
2. Description of Related Background Art
A conventional spectrum analyzer of this type, shown in FIG. 5 by way of example, displays a frequency spectrum in the following manner. An input signal is supplied to a plurality of band-pass filters 21 to 27 each having a different center frequency. The outputs of the band-pass filters 21 to 27 are supplied to, and rectified by, associated rectifiers 28 to 34. The rectified outputs from the rectifiers 28 to 34 are sequentially sampled by an analog switch circuit 36 in synchro with timing signals from a timing signal generator 35, and converted into digital data by an A/D converter 37. The digital data are displayed on a level meter 38 as a bar graph in synchro with the timing same as that used for the analog switch 36. In FIG. 5, reference number 40 represents a level meter driver, and 40 represents a timing driver which receives a timing signal from the timing signal generator 35, and synchronizes the timing when each bar is displayed on the level display 38, with the timing used for switching the analog switch 36.
In displaying a frequency spectrum on a spectrum analyzer, the afterimage effect of human eyes is utilized. Generally, a visually proper frequency spectrum can be displayed if the analog switch 36 is switched at the sampling period of several tens to several hundreds Hz.
There is also known a spectrum analyzer using a microcomputer or the like, wherein A/D converted level data are stored in a temporary memory and displayed on a level meter at the different timing from the sampling timing used for the analog switch 36.
In order to display a visually smooth response-frequency curve on a spectrum analyzer, it has been necessary to make the number of frequency divisions large. The number of band-pass filters, rectifiers increase correspondingly, and a large scale analog switch is used. The space for these circuit elements of the spectrum analyzer becomes large, and the spectrum analyzer becomes expensive.
It is therefore an object of the present invention to provide a spectrum analyzer capable of providing a large number of frequency divisions with a small number of band-pass filters.